1. Field of the Invention
This patent specification relates to downhole acoustic measurements in connection with downhole fluid sampling and testing. More particularly, this patent specification relates to systems and methods for making and analyzing acoustic measurements in combination with a downhole hydraulic fracturing tool system.
2. Background of the Invention
In the oilfield service industry, characterizing commercially viable reservoirs of hydrocarbons is a main objective of well logging services. Downhole sampling and testing tools such as the Modular Dynamic Formation Tester (MDT) from Schlumberger are used during the well logging phase to gain a more direct assessment of the production characteristics of the accumulation. In one common configuration, the MDT is arranged with dual packers set against the borehole wall, thereby creating an isolated fluid interval in the annulus bounded by the tool outer surface, the borehole wall, and the two inflatable packers. Additional modules within the MDT enable controlled changes in pressure and flow in the interval. According to this conventional configuration, the pressure is monitored by pressure gauges designed to record the average pressure approximately once per second. During some types of operations, for example fluid sampling operations, fluid is drawn from the annular packed-off region into the tool. Although the onset of a change in the fluid properties of the annular region is often eventually detected by sensors within the tool body, it is often desirable to improve evaluation of the such changes and to obtain the information more quickly.
In some types of testing operations, rapid changes in pressure sometimes occur. For example, in a microhydraulic fracturing test, the interval is pressurized by pumping fluid into the annulus until a tensile fracture begins. The initiation is recorded by a breakdown on a pressure-vs-time record sampled at about one sample per second. It is desirable to evaluate these rapid changes in greater detail. Further detail of acoustic measurements during microhydraulic fracturing testing and in connection with other downhole sampling and testing tool systems is disclosed in International Patent Application PCT/US08/87970, filed Dec. 22, 2008 which is incorporated by reference herein. It is desirable to further improve the evaluations of the formation when performing microhydraulic fracturing testing. Additionally since the sampling and testing tools have pumps, valves and many other moving parts, it is desirable to more effectively monitor the operation of these moving parts.